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>cool new johto mons are locked to post games
>old evolution stones locked to post games so if you do pick up a kanto mon in johoto that evolves with them (bellsprout, growlithe, vulpix, ect) you have to wait for post game to fully evolve them.
>wild kanto pokemon are so underleveled compared to your team that you'll never want to have to train them up
>trainers other than gym leaders are also under leveled compare dot the elite four you just beat
having two regions in the game was a mistake.